Add peppers, olive oil, vinegar, sugar, granulated garlic, salt and pepper to a large skillet and toss to coat. Place the skillet over medium-high heat and saute the peppers until they start to get slightly tender, 3 to 5 minutes. Nestle in the sausages amongst the peppers and lower the heat to low, then cover and gently simmer until the sausages are about 145 degrees F, 5 to 10 minutes.
Meanwhile, preheat a grill or grill pan over medium-high heat. Remove the sausage from the skillet and grill until charred and the internal temperature reaches 165 degrees F, about 10 minutes. Place back in the skillet with the mini sweet peppers and serve.